Processes for forming aldehyde products by the hydroformylation reaction of an olefinic compound with carbon monoxide and hydrogen in the presence of a rhodium-tertiary organophosphine complex hydroformylation catalyst are well known in the art. Of particular interest are those hydroformylation reactions designed to produce aldehydes at low pressures, such as disclosed, e.g., in U.S. Pat. Nos. 3,527,809; 4,148,830; 4,247,486; and 4,731,486.
Commercial experience has shown that, even in the substantial absence of extrinsic catalyst poisons, rhodium-tertiary organophosphine complex catalysts lose activity (i.e. become partially deactivated) during the course of continued prolonged hydroformylation, and such is commonly referred to as intrinsic deactivation. While it is difficult to ascertain the precise reasons for such lose in activity, such intrinsic deactivation is believed to be due in a large part to the combined effects of a number of processing conditions, e.g., reaction temperature, reactant partial pressures, the phosphine ligand, the ligand to rhodium mole ratio, and rhodium concentration employed, which lead to the formation of inactive rhodium complex clusters. Since the variables significant for such catalyst instability are also variables essential for the hydroformylation, obviously such deactivation can not be totally avoided, although it can be controlled or minimized. However, eventually the activity of the catalyst will decrease to such a point that it is no longer desirable to operate the hydroformylation process, and the catalyst will either have to be reactivated or discharged and replaced with fresh catalyst. Accordingly, reactivation of such partially deactivated rhodium complex catalysts remains highly important to the state of the art in view of the high cost of rhodium, as seen by the many various methods that have been proposed by the prior art for minimizing or preventing such deactivation and/or reactivating the partially deactivated rhodium complex hydroformylation catalyst.
One of the more recent reactivation procedures, as disclosed in U.S. Pat. No. 4,861,918, resides in the treatment of the solubilized partially deactivated rhodium-tertiary organophosphine complex hydroformylation catalyst with various organic reagents, such as acetylenic compounds containing halogen, carboxylate, sulfonate or phosphonium radicals, to achieve a hydroformylation catalyst that is more chemically active than the initial partially deactivated catalyst starting material, said increase in reactivity exhibiting itself upon elimination from the treated catalyst product any hydroformylation catalytic inhibitor that might have been formed during the treatment procedure. However, while said treatment procedure has been found to be quite beneficial in restoring the activity of such partially deactivated rhodium catalysts, the heretofore proposed acetylenic reactant compounds, such as propargyl acetate, are for the most part not readily commercially available. Moreover such proposed acetylenic reactants due to their high functionality (i.e. acetylenic and salt groups) may be subject to various undesirable side reactions that may adversely affect the desired reactivation of the treated catalyst and/or its ultimate end use. Thus there is still a desire in the art for a method which would permit restoration of such partially deactivated rhodium catalyst activity with organic reagents that have greater commerical availability in comparison to the acetylenic compounds, such as propargyl acetate, disclosed in U.S. Pat. No. 4,861,918.